[llvm] [DebugInfo][SimpleLoopUnswitch] Fix missing debug location updates (PR #97662)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -0,0 +1,75 @@
+; RUN: opt -passes='simple-loop-unswitch<nontrivial>' -S < %s | FileCheck %s
+
+define i32 @basic(i32 %N, i1 %cond, i32 %select_input) !dbg !5 {
+; CHECK-LABEL: define i32 @basic(
+
+; Check that SimpleLoopUnswitch's unswitchNontrivialInvariants() drops the
+; debug location of the hoisted terminator and doesn't give any debug location
+; to the new freeze, since it's inserted in a hoist block.
+; Also check that in unswitchNontrivialInvariants(), the new br instruction
+; inherits the debug location of the old terminator in the same block.
+
+; CHECK:       entry:
+; CHECK-NEXT:    [[COND_FR:%.*]] = freeze i1 [[COND:%.*]]{{$}}
+; CHECK-NEXT:    br i1 [[COND_FR]], label %[[ENTRY_SPLIT_US:.*]], label %[[ENTRY_SPLIT:.*]]{{$}}
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OCHyams wrote:

Glancing at the IR, the old behaviour (new cond branch gets uncond branch location) looks fine, but I think this change does make sense - just to make sure I'm reading this right, is the argument here that the conditional branch above is essentially a `select` from within the loop that's been hoisted out? And that in this case the new branch would get the `select`'s source location, but because it has been hoisted out the loop we should actually drop it.

https://github.com/llvm/llvm-project/pull/97662